1. Field of the Invention
The present invention relates to a method and an apparatus of sampling a suction effusion fluid and more particularly, to a method of sampling a suction effusion fluid by sucking a body fluid from the skin surface of a human body for the purpose of determining the in-vivo substances, and a sampling apparatus used for the sampling method.
2. Description of the Related Art
A suction effusion fluid is an extremely small quantity of fluid obtained by vacuum-sucking a skin whose horny layer is removed. This fluid is considered to be an interstitial fluid in a subcutaneous tissue or a blood filtered and effused through the wall of a capillary.
In recent years, it has been clarified by many years of researches that the suction effusion fluid is a body fluid similar to a blood serum, and that the concentrations of some constituents such as glucose and lactic acid in the suction effusion fluid have a good correlation with the concentrations in the blood. This is disclosed in a paper, the 35th Japan Soc. ME & BE Conference, pp. 474, May, 1996, which was written by Murakami, Kaneyoshi, Nishida, Twasaki, Kawakami, Kayashima, Arai, and Kikuchi.
Because sampling of a suction effusion fluid is performed without viewing the blood, the physical and mental pain or a subject is little and the possibility of infection is low compared to those in blood drawing. Because the sampled suction effusion fluid contains no blood corpuscle constituents, the constituents of a body fluid can be continuously determined with ease without the need for a special treatment such as anticoagulation. Accordingly, if the suction effusion fluid is used for determination of the living organism related substances, there arises an advantage that the physical and mental pain associated with blood drawing is reduced and thus, the constituents of the body fluid of women and infants, with whom blood-gathering is difficult, can easily be determined.
Until recent years, sampling of the suction effusion fluid had been made after removing the horny layer by such a method as the tape stripping method. In this conventional method, however, there are a problem that much labor and time are required to remove the horny layer and that a time period of two weeks or so is required for regeneration of the tissue of the horny layer.
To solve this problem, an improved sampling method of a suction effusion fluid, which eliminates the need for removing the horny layer, has been offered. This method is disclosed in, for example, the Japanese Patent Application No. 7-241774 filed in September 1995.
FIG. 1 shows a sectional view of a sampling apparatus of a suction effusion fluid used with the improved method disclosed in the Japanese Patent Application No. 7-241774 filed in September 1995.
As shown in FIG. 1, this sampling apparatus is comprised of a suction cell 503 having a suction port 501 at one end and an aperture 502 at the other end, and a channel plate 504, fitted to the aperture 502. The aperture 502 is opposed to a human skin and the channel plate 504 is directly contacted with the skin on sampling.
On the side of the suction port 501 of the channel plate 504, a plurality of channel grooves 505 are radially formed from the center of the plate 504. A plurality of through holes 506 are formed to extend axially in the plate 504. The through holes 506 are connected to the channel grooves 505.
On the side of the aperture 502 of the channel plate 504, a plurality of protrusion needles 507 are formed. Each of the protrusion needles 507 is formed by a protruded edge of the plate 504 in the vicinity of a corresponding one of the through holes 506. The length of the needles 507 is approximately 50 .mu.m, and the diameter of the through holes is in the range of 50 to 200 .mu.m.
Sampling of an effusion fluid with this apparatus in FIG. 1 is made in the following way.
First, in a portion of the skin where an effusion fluid is to be sampled, the aperture 502 of the suction cell 503 is brought into tight contact with the horny layer. Then, the inside of the suction cell 503 is evacuated from the suction port 501. With this evacuation, the protrusion needles 507 bite the skin surface to pierce the horny layer and as a result, an interstitial fluid in the skin is effused through the horny layer as an effusion fluid. The sucked effusion fluid is collected to the suction port 501 through the holes 506 and the grooves 505, and is taken out to the outside of the suction cell 503.
The improved sampling method of a suction effusion fluid using the sampling apparatus shown in FIG. 1 eliminates the need for removal of the horny layer, and substantially shortens the pretreatment time in sampling and the time period until the tissue is regenerated. Therefore, the above problems of the conventional method that removes the horny layer are solved. However, this improved sampling method has the following problems.
A first problem is that a suction effusion fluid is effused with a low efficiency. One reason is that only the portions of the skin with which the through holes 506 are contacted are sucked and therefore, the area of the surface layer of the skin contributing to the effusion is small, when compared to that with the conventional method where the horny layer is removed. Another reason is that the gap between the protrusion needles 507 serving as an effusion path for the effusion fluid and the opposing horny layer is narrow, when compared to that with the conventional method.
A second problem is that penetration of the horny layer by the protrusion needles 507 tends to be insufficient. This is because the skin is deformed so that the piercing pressure is distributed, which results from the piercing of the needles 507 is made by a semi-static behavior consisting of pressing and suction.